Projection lamp and mounting therefor



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Oct. 18, 1949. w. GRIFFIN 8 ,31

PROJECTION LAMP AND. IOUNTIIW THEREFOR Filed In, 21. 1946 l'nvervtor: Wilfrid Gr'if'fin,

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of relying Patented Oct. 18, 1949 PROJECTION LAMP AND MOUNTING THEREFOR Wilfrid Griflin, Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application May 21, 1946; Serial No. 671,353

7 Claims. (Cl. 240-413) This invention relates to light projection apparatus useful especially for picture'projection, and is concerned with electric lamps for this purpose, and with their relation to light directing means of the projection apparatus.

Lamps commonly used for motion picture projection consist of a concentrated light source, usually of coiled incandescent filament type, in

' a tubular light .transmitting bulb or envelope,

usually of heat-resistive hard glass to stand the high temperature to which the lamps are subjected in use. It is very important thatin use the concentrated light source be definitely and correctly positioned with respect to the primary light directing means of the apparatus, commonly consisting of a reflector behind the lamp and a light condenser of refractive character in front of it. It is also very desirable that the light source be properly and definitely located with respect to'the tubular envelope wall, or, at least, with respect to the portion of the wall through which light reaches the condenser.

'It has hitherto been sought to locate and position the light source with respect to the tubular envelope and thelight-directing means by our-'- ploying a. prefocused base," or an equivalent envelope part: i. e., a mounting structure connected or attached to the light source and to the tubular lamp envelope in a carefully determined relation'to them. This not only demands a base of exacting dimensional accuracy and a socket of similar accuracy, which must be accurately placed with respect to the light-directing means of the projection apparatus, but also requires a prefocusing operation by a skilled operator during the manufacture of the lamp to assure the proper relation of the base to the light source and structure prefocused relative to the light source and the envelope wall, I orient and position the light source only in relation to the envelope wall; or, alternatively, I specially orient and position certain portions of the envelope wall relative to the light source. I then orient and position the lamp relative to the light-directing and other partsof the projection apparatus by the envelope wall, or by the specially oriented and positioned portions of this wall. Thus the base becomes a mere carrier of contact terminals for making electrical connections to the lamp; or it may even be dispensed with by making such connections directly'to the usual external lamp leads as contact terminals. In any case, the contact terminal and connector features of lamp and projection apparatus can be so simplified and reduced in bulk as not to obstruct or interfere with the supply of cooling air. Moreover, the removal and replacement of a failinglamp becomes much easier and quicker.

Various other features and advantages of the invention will appear from the following description of species thereof and from the accompanying drawings in which:

Fig. 1 is a vertical section, partly in elevation, of a lamp and associated mounting and lightdirecting means according to mylnvention; Fig.

2 is a section on the line 22 of Fig. 1 with the the envelope. The difiiculties of such accuracy as regards both base and socket are greatly enhanced by the considerable distance from the base to the light source: i. e., any slight angular error in the alignment of base or socket gives rise to a greatly magnified linear error in the position of the light source with respect to the envelope and the light-directing means. Also, the mere bulk of the base and the socket makes it difiicult to cool the parts efiectively, by obstructing the desired upward flow of cooling air about and along the lamp envelope and the associated parts of the projection apparatus. The danger of overheating motion picture film travelling close in front of the condenser lens(es) is well known.

My invention makes it possible to overcome or avoid the above mentioned difiiculties.

on a base or other such mounting Instead lamp shown in elevation; Fig. 3 is a horizontal section on the line 3-3 of Fig. 1; and Fig. '4 is a fragmentary elevation of a modified form of lamp construction according to the invention.

The drawing shows a projection lamp l of an ordinary type comprising an elongated or tubular vitreous envelope or bulb 2 enclosing a concentrated light source 3 in the form of a compactly arranged tungsten wire filament helically coiled in a number of upright interconnected sections and forming part of the lamp mount 4. The coils 3 may lie in a single plane, or they may alternate between parallel planes as shown. The

current leads 5, 5 to the filament 3 may penetrate the envelope 2 through a. press" or other stem seal 6. The upright tubular lamp I is mounted in a lamp housing 1 of a projection apparatus, the lamp being positioned between reflecting and retracting light-directing means at opposite sides of the envelope 2, the former consisting of a spherical concave reflector 8 and the latter of a light-condenser 9. The lamp housing I is provided with opposed circular apertures III, II to receive and hold the reflector 8 and condenser 9, respectively. The reflector 8 is mounted in a tubular housing or' barrel I2 which screws into a threaded socket l3 fastened on the inner side of the rear wall ll of the lamp housing I. The light condenser 8 is of a well known type comprising a pair of lenses l5, l5 mounted within a tubular housing or barrel l6 and held at a deflnite correct distance apart, against the internally shouldered ends of the barrel l6, by a helical compression spring l1 disposed between and engaging the lenses. In general, it is desired that the light center of the source 3 lie at coincident foci of reflector ,8, and of condenser 9 or its lens adJacent the source 3.

It will be understood that as thus far described, these and various other features of the lamp and of the projection apparatus form no part of my present invention, and may, indeed; be greatly varied.

As shown in Figs. 1-3, the lamp is supported in place within the lamp housing 1 by opposed holder means engaging opposite sides of lamp envelope 2 and comprising positioning means l8 for vertically aligning the lamp and resilient clamp means IQ for holding the lamp in engagement with the said positioning means. The positioning means l8 comprise a vertically disposed plate 28 apertured at 2| to snugly receive the condenser housing IS. The plate 28 is secured to the rear closure ring 22 of the condenser housing l8, as by welding for instance, and is fixed in proper rotative position about the axis of the cylindrical condenser housing It by means of a locating pin 23 which snugly-fits into a. hole 24 in the lamp housing 1. The plate 2|) is provided with upper and lower vertically-aligned rounded bulb-engaging buttons or protuberances 25, 25 which may take the form of round-headed rivets with their shanks riveted through the plate 20. The envelope wall 2 is provided with corresponding surface configurations providing positioning shoulders in the form of socket recesses or depressions 26, 21 spaced longitudinally of the envelope on opposite sides of and definitely located with respect to the light source 3 therein, in which recesses the positioning elements or buttons 25, 25 engage to thus orient the light source 3 angularly about the vertical lamp axis and also position the lamp I and light source 3 vertically relative to the light-directive means 8, 9. While the lower envelope wall indentation or recess 26 is substantially of spherical or dimple shape strictly conforming to'the lower button 25, the upper indentation or recess 21 is shown as elongated vertically, to take care of any slight variation in the vertical distance between the :buttons 25, 25 or between the recesses 26, 21.

The clamp means I! which holds the lamp in engagement with the positioning means I8 comprises a pair of vertically-spaced closed loop plate springs 28, 28 mounted on and projecting forwardly from the reflector socket |3 of the lamp housing. The springs 28, 28 engage the rear side of the tubular lamp envelope 2 at spaced points therealong on either side of the light source 3 therein, thus resiliently urging the lamp forwardly against the positioning means l8 withthe matching protuberances and depressions 25, 26 and 21 on the positioning means and lamp envelope in interlocking engagement. The upper spring loop 28 is provided with a substantially flat bulb-engaging portion 38 while the lower spring loop 29 is provided with a rounded bulbengaging button or protuberance 3|, similar to the buttons 25, 25, which engages in a matching recess or depression '32 in the lamp envelope wall 2. The button 3|, engaging in the envelope recess 32 located on the side of the envelope opposite to that side engaged :by the buttons 25, thus serves to lock the lamp in proper lateral position so as to laterally line the light source 3 with the optical axis of the light-directive means 8, 9. Like the upper recess 21 in the front side of the lamp envelope, the recess 32 is elongated vertically to take care of any slight variation in the vertical position of the button 3| or the recess 32 itself.

To facilitate insertion of the lamp I from beneath, upward into the lamp housing 1 and into proper engagement with the positioning elements or buttons 25 and 3|, a top stop 33 may be provided for engaging the upper end of the lamp envelope. The said top stop 33 comprises a hairpin-shaped wire loop having its looped end portion bent at right angles to overlie the lamp l and having its upright portion engaged slotwise with the shanks of clamping screws 34, 34 which are screwed into the lamp housing 1 to thereby fasten the wire loop thereto.

Besides the coaction of the buttons 25, 3| and the matching sockets 26, 21 and 32, Fig. 4 illustrates another novel feature with which the lamp envelope 2 may be provided. This is a special window portion 35 registering with the light condenser 9 and made relatively unreflective of light, thus reducing very greatly the reflection losses due to oblique incidenceof light from the source 3 on the envelope wall portion corresponding to the condenser 9. By suitable optical treatment of the window portion '35 the reflection losses thereat may be reduced by approximately per cent, since reflection occurs at both the inner and outer surfaces of the glass. For this purpose, the window portion 35 may be coated inside or out, or both, with a non-reflecting fllm of magnesium fluoride (MgFz), for example. Other suitable non-reflective materials for this purpose are also known in the optical art.

Another means of reducing reflection losses at the window 35 is to mold or otherwise form this portion of the envelope wall flat, or at any rate with greatly reduced curvature, as shown in Fig. 4. By molding the window 35- concurrently with the recesses 26, 21 and 32 and locating the light source 3 in definite relation to the window and recesses, a definite fixed distance of the light source from the window and of both from the condenser may be maintained. Of course, a window portion 35 of the envelope 2 may be either treated or flattened, or both.

The direct advantage of flattening the window 35 will be better appreciated when it is realized that while light incident on glass in a direction normal to its surface suffers a reflection loss of only about 5 per cent, this loss increases very much as the angle of incidence becomes more and more acute, e. g., for a variation of incidence of 10 degrees from the perpendicular, the internal reflection loss is about 15 per cent, and the ex- 1 ternal loss about the same. A further advantage accrues in the diminished heating of the envelope wall due the energy of absorbed light.

As shownin Figs. 1 and 2, the lower end of the envelope 2 is equipped with a base 36 comprising a sheet metal shell in which apertured flat projecting contact prongs 31, 31 are insulatively mounted, constituting a familiar type of male connector. A corresponding known type of female connector 38, with contact-equipped openings for the prongs 31, 31, is connected to the flexible supply circuit cord 39. Thus, the bulbheld lamp supports the parts 36, 38, instead of being supported by them as in prior devices. This fact and the reduced bulk of the parts 36, it greatly improve the cooling of the lamp l and the associated parts by upfiow of air or other cooling medium through the lamp housing I, which may be assured and augmented by any suitable means,

such as by a fan 40 revolving about a vertical axis directly below the part 38 and a lamp chimney which surrounds the lamp and which may comprise two half sections ll, 42 supported from the lamp housing I.

While I have shown and described the preferred form of the invention, it is obvious that other modifications are possible within the scope of the appended claims. Thus, the arrangement of the bulb-supporting protuberances 25, 3| and matching depressions 26, 21 and 32 may be reversed by providing one or more of the protuberances on the lamp envelope 2 and the corresponding depressions on the bulb holder. Likewise, the protuberances 25, II and depressions 26, 21 and 32 may be of a shape other than that illustrated, for instance, they may be of matching ridge and groove shape.

lamp opposite the light source, and opposed holder means engaging opposite sides of the lamp envelope to support the lamp in place, said envelope and holder means being provided with matching protuberances and depressions for holding the lamp with its light source positioned in definite relation to said light-directing means, said matching protuberances and depressions being located at one side of the envelope at spaced points therealong oppositely remote from the light source therein.

2. In combination, an electric lamp comprisin a light source in an enclosing tubular envelope, said envelope having its outer wall surface formed at one side with surface configurations located at spaced points therealong on either side of and in definite relation to the light source therein, light-directing means at one side of the lamp opposite the light source. and opposed holder means engaging opposite sides of the lamp envelope to support the lamp in a predetermined position with respect to said light-directing means, said holder means comprising stationary positioning elements interlocking with the said envelope wall configurations on one side of the envelope, and resilient means engaging the opposite side of the envelope to maintain the said envelope wall configurations in interlocking engagement with the said positioning elements.

3. Projection apparatus comprising in combination coacting reflective and condensing refractive light-directing means separated to accommodate therebetween an electric lamp comprising a concentrated light source mounted in a tubular envelope, holder means for enga g the tubular envelope at zones oppositely remote from the light source and from said light-directing means but at the side of said envelope where one of said lightdirecting means is located, and additional holding means for engaging said tubular envelope at its opposite side.

4. An electric lamp comprising a tubular envelope containing a concentrated light source, the wallet said envelope being formed with surface configurations providing integral positioning shoulders spaced relatively widely apart longitudinally of the bulb, and the said light source being located in an accurately predetermined position with respect to and between the said spaced positioning shoulders.

5. An electric lamp comprising a tubular envelope containing a concentrated light source, the

wall of said envelope being formed with surface configurations providing integral positioning shoulders aligned and spaced relatively widely apart longitudinally of the bulb, the said light source being located in an accurately predetermined position with respect to and between the said spaced positioning shoulders, the envelope wall being formed with additional surface configurations providing positioning shoulders located at points on said envelope longitudinally between the first-mentioned positioning shoulders and diametrically on the opposite side of the envelope.

6. An electric lamp comprising a tubular envelope containing a concentrated light source, the wall of said envelope being configurated to provide integral engagement dimples at points spaced relatively widely apart longitudinally of the bulb, the said light source being located in an accurately predetermined position with respect to and between the said spaced engagement dimples.

7. An electric lamp for light projection apparatus comprising a concentrated light source, an enclosing tubular envelope having a specially unrefiective light-transmitting window portion for coaction with a light condenser of the projection apparatus and adapted to engage holder means at zones spaced longitudinally of the envelope and oppositely remote from the lightsource therein, and surface configurations on the wall of said envelope for engaging with corresponding positioning elements on said holder means to thereby position the lamp with its said window portion in registry with said light condenser.

WIIFRID oau'rm.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,675,690 Bohner July 3, 1928 FOREIGN PATENTS Number Country Date 350,816 Great Britain June 18, 1931 

